In digital TV, the power levels of channels that are adjacent to the wanted channel can be 30 dB to 40 dB higher than the wanted channel. Part of this power is removed by the tuner, yet a significant part of this appears at the input of the analog to digital (A/D) converter (ADC) of the digital demodulator. The automatic gain control circuit has to adjust the power level of this composite (wanted+adjacent) signal at the input of the ADC to get optimum receiver performance.
In emerging DTV standards, a channel may be time-multiplexed between different services. For example, in DVB-T2 there are Future Extension Frames (FEFs) which are intended to carry other services. Although not limited in this respect, one such service already identified is the signaling for transmitter identification. The power levels of different services may not be the same.
Hence in DVB-T2, the power level of FEFs may well be different from that of other frames. Although this is not a problem with current systems, it is a problem that is likely to occur in the future when DVB-T2 type transmissions with multiple services are widely adopted.
Thus, a critical need is prevalent for apparatus, systems and methods that enable DTV demodulators to overcome this potential problem.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements.